6-iodo-2-oxindole is an important intermediate for the production of pharmaceutically active ingredients. The synthesis of this intermediate has been described in the literature before and is quite challenging. Therefore there is a strong demand for efficient methods to manufacture 6-iodo-2-oxindole in the high quality needed for pharmaceutical intermediates.
In current literature several routes to manufacture 6-iodo-2-oxindole have been described.
WO 2007008985 describes the synthesis of 6-iodo-2-oxindole via catalytic electrophilic aromatic iodination of 6-bromo-2-oxindole using sodium iodide in the presence of a copper catalyst (Scheme 1). The disadvantage of this approach is the fact that 6-bromo-2-oxindole is not directly commercially available as a bulk chemical. Additionally the use of large amounts of a copper catalyst, the use of dioxane as solvent and several reaction additives which are only available on laboratory scale disqualify this approach for commercial production.

JP 2011207859 describes the synthesis of 6-iodo-2-oxindole from 1,4-diiodo-2-nitro-benzene via two steps of reaction. The disadvantage of this process is again the use of a starting material that is not commercially available on larger scale, therefore this process is also disqualified for use for commercial production of 6-iodo-2-oxindole (Scheme 2).

Therefore there is a strong need for a novel process to manufacture 6-iodo-2-oxindole, which allows to use commercially available bulk chemicals as starting materials and which renders the desired product in high quality and good chemical yield.